Stormwater management is arguably the most significant environmental benefit of GRs, allowing for water retention, water treatment, volume reduction, and evaporation. Extensive GRs can be designed as part of newly constructed buildings or retrofitted into existing buildings. Because of the shallower substrate depth, plant choices for extensive GRs are often limited to drought-tolerant and/or shallow-rooted species, such as herbs, grasses, mosses, and succulents such as stonecrops ( Sedum sp.) ( Farrell et al., 2013). In contrast, extensive GRs are defined by a substrate depth of less than or equal to 6 inches. Intensive GRs are incorporated into a building structure's design, and are generally impractical as a retrofit because of the substrate depth and weight, which demand higher structural requirements. GRs fall into two broad categories: “intensive” and “extensive.” Intensive GRs have more than 6 inches of planting substrate and can thus support a diversity of vegetation including small trees, shrubs, or forbs. Green roofs are an urban design strategy that improves living environments while supporting ecological, economic, and ornamental purposes ( Oberndorfer et al., 2007). Keywords: maintenance practices plant cover evaluation stormwater management weeds Green roof maintenance costs ranged from $0.13/ft 2 to $3.45/ft 2 per year, and were greater on sites with more weeds and frequent hand watering. Plants persisting on GRs included several species of stonecrop ( Sedum sp.), but flame flower ( Talium calycinum) and ice plant ( Delosperma basuticum) were also present in high populations on at least one roof each. ![]() Results showed a trend that irrigation increased plant cover. Green roof age, substrate organic matter, and modular planting methods were not correlated with greater plant cover. No single design or maintenance factor was highly correlated with increased plant cover. Survey respondents ranked weed control as the most problematic maintenance task, followed by irrigation, pruning, and debris removal. Relationships among plant performance and environmental and physical site characteristics, and maintenance practices were evaluated. Vegetation cover on each site was characterized. Green roof maintenance professionals were surveyed to assess plant performance, maintenance practices, and maintenance costs. The objective of this study was to assess plant cover, site conditions, and maintenance practices on 10 extensive GRs in the Research Triangle Area of North Carolina. Compared with traditional roofing, green roofs (GRs) have quantifiable environmental and economic benefits, yet limited research exists on GR plant survival, maintenance practices, and costs related to plant performance.
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